Because of its ready availability and because of its relatively low cost and potential for reducing particulate emissions, compressed natural gas is a promising candidate for fueling diesel engines. Conventional methods of fueling diesel engines by premixing air and natural gas appear to be inherently unsuitable for part load operation, at which the fuel-air mixture flammability suffers, efficiency drops substantially and emissions become excessive. In addition there is the problem of detonation under certain load conditions. These factors generally impose a limit on the feasible substitution of diesel fuel by natural gas in transport engines operating over a wide range of load and speed.